1. Field of the Invention
The present invention relates to a method of joining terminals to a printed circuit board by soldering.
2. Description of the Background Art
Various methods exist for joining terminals to a printed circuit board. For example, Japanese Patent No. 2768141 describes a technique using laser welding.
Instead of laser welding as in the aforementioned Japanese Patent, soldering using laser heating can also be employed to join terminals to a printed circuit board.
In soldering, a flux may be used for purposes such as prevention of oxidation and removal of oxides. Or, a silicone gel may be applied onto a printed circuit board after soldering for purposes such as assurance of insulation and shock absorption. There are also cases where a flux and a silicone gel are used in combination; for example, soldering using a flux is followed by the application of a silicone gel on a printed circuit board.
In the combined use of a flux and a silicone gel, however, hardening of the silicone gel may easily be inhibited by the influence of flux residues on a printed circuit board. Thus, a cleaning process is required for removal of flux residues from on top of the surface of a printed circuit board.
A cleaner is however an expensive and large-scale equipment; thus, the introduction of a flux cleaning process will complicate the configuration of a manufacturing line and therefore will increase equipment expenses.
From the above, fluxless soldering techniques have also been devised. The fluxless soldering techniques need no flux cleaning process from the very first, and thus, eliminate the need for a cleaner, in which case the hardening of a silicone gel is not inhibited. Such techniques include performing soldering in an atmosphere of a gas mixture of an inert gas such as nitrogen and a reducing gas such as hydrogen to reduce and remove oxides from solder surfaces. Here, the gas atmosphere is realized by blowing a gas onto solder joints or by performing soldering within a gas chamber filled with a gas.
However, the problem with the case of blowing a gas is that solder and terminals are cooled by gas injection and thus the solder is hard to melt. On the other hand, the case of creating a gas atmosphere within a gas chamber does not have such a cooling problem, but in this case, an insertion port for the introduction of a soldering jig and an opening for the admission of a laser beam must be provided within a gas chamber. Since a leakage of gas from such an insertion port for a jig and such an opening for a laser beam is inevitable, an increasing supply of gas becomes an issue.